Explosion-proof lighting unit



March 26, 1957 A. 1. APPLETON 2,786,936

EXPLOSION-PROOF LIGHTING UNIT Fiied July 22, 1950 3 Sheets-Sheet lInventor afthur I cynleton 6a,, wmmm March 26, 1957 A. l. APPLETON2,786,936

EXPLOSION-PROOF LIGHTING UNIT Filed July 22, 1950 5 Sheets-Sheet 2 March26, 1957 l. APPLETON EXPLOSION-PROOF LIGHTING UNIT 3 Sheets-Sheet 3Filed July 22. 1950 lnu en tor arlhurl @242 ton United States atent O MEXPLOSION-PRUOF LIGHTING UNIT Arthur I. Appleton, Northbrook, Ill.Application July 22, 1950, Serial No. 175,430

9 Claims. (Cl. 240-112 The present invention relates to electricallighting units in general and more specifically to a novelexplosionproof lighting unit which finds particular but by no meansexclusive utility in such places as refineries, chemical plants, andother installations where inflammable or explosive mixtures of gases,vapors, or dust are present in the atmosphere. This application is acontinuationin-part of my earlier application Serial No. 124,051, filedin the United States Patent Olfice on October 28, 1949 and nowabandoned.

In the construction of an explosion-proof lighting unit, considerationmust be given even to remote possibilities of failure. For example, anelectrical breakdown occurring within the unit or the power supplyconduit leading thereto could result in the creation of an are capableof igniting explosive or inflammable gaseous mixtures which almostinevitably filter in from the surrounding atmosphere. Unless thelighting unit is properly designed, the resulting leakage of flametherefrom could easily ignite inflammable or explosive mixtures ofgases, vapors, or dust particles in the atmosphere around the unit.Consequently, the potential arcing portions of the unit must becompletely housed and segregated from such surrounding atmosphere.

One object of the present invention is to provide a novel and improvedexplosion-proof lighting unit which will be extremely light in weightbut susceptible of use with a high margin of safety in very severeapplications.

Another object is to provide a lighting unit of the foregoing typecapable of avoiding the occurrence of excessive internal peak pressuresby rapidly dissipating gas pressure from the interior of the unit intothe surrounding atmosphere with no danger of igniting the same.

A further object is to provide an explosion-proof lighting unit of thecharacter set forth and wherein the fixture portion may be attached toor detached from its supporting canopy by a simple mechanical operationperformed entirely without danger of exposed arcing.

Another object is to provide an explosion-proof lighting unit ofrelatively simple, inexpensive construction which will function with ahigh degree of electrical safety and yet be susceptible of economicalmanufacture under mass productive methods.

Other objects and advantages of the invention will become apparent asthe following description proceeds, taken in the light of theaccompanying drawing, wherein:

Figure 1 is an enlarged fragmentary vertical sectional view through anillustrative explosion-proof lighting unit embodying the presentinvention.

Fig. 2 is a perspective view showing the fixture portion of the unit ofFig. 1.

Fig. 3 is an enlarged perspective view detailing the body portion of theunit shown in Fig. 1.

Fig. 4 is an enlarged fragmentary vertical sectional view illustratingthe relation between certain components of the unit of Fig. 1 as thefixture is assembled upon the canopy.

Figs. 5 and 6 are enlarged transverse sectional views metallic materialhaving flame arresting properties.

2,786,936 Patented Mar. 26, 1957 through the unit of Fig. 1 but taken inopposite directions in the plane of the line 5-5, 6-6.

Fig. 7 is an enlarged transverse setcional view through the unit shownin Fig. 1 but taken in the plane of hue 7-7.

Fig. 8 is an enlarged fragmentary vertical sectional view through amodified explosion-proof lighting unit also embodying the presentinvention.

Figs. 9 and 10 are transverse sectional views taken through the modifiedunit of Fig. 8 but in the planes of 99 and 10--10, respectively.

While the invention is susceptible of various modifications andalternative constructions, certain preferred embodiments have been shownin the drawings and will be described below in considerable detail. Itshould be understood, however, that there is no intention to limit theinvention to the specific forms disclosed, but on the contrary, theintention is to cover all modifications and alternative constructionsfalling within the spirit and scope of the invention as expressed in theappended claims.

Referring more specifically to Fig. 1, it will be perceived that theinvention is there shown embodied in an illustrative lighting unit 20comprising a hollow supporting canopy 21 together with a fixture 22mounted in depending relation thereon. The canopy 21 is fashioned with aneck 24 of reduced diameter and which is readily attachable to asuitable stem mounted upon a ceiling or other overhead support. The neck24 merges with an outwardly flared portion terminating in an annularstop shoulder 25 and an externally threaded depending skirt 26. Powersupply wiring (not shown) may be led through the neck 24 to terminalblock 28 located within canopy terminal chamber 29.

The fixture 22 is organized upon a hub-like body 30 having an internallythreaded upper end portion 31 which is susceptible of detachableengagement with the threaded skirt 26 of the supporting canopy. Theopposite end of the body 30 terminates in a threaded annular flange 32which is adapted to carry a globe ring 34. The latter is provided with aseries of circumferentially spaced notches 35 to facilitate turnng.Clampingly secured to the flange 32 of the body by the globe ring 34 anda gasket 36 :is a transparent or translucent globe 38 of heat resistantglass which possesses a high degree of mechanical strength. The globe38, together with the body 30, defines a lamp chamber 39 which -in thepresent instanceis adapted to house an incandescent lamp 40. Spaced fromthe globe 38 but nested about it is a cage-like guard 41 fixed to theglobe ring 34. Also fixed to the latter and disposed in surroundingrelation with the globe and the guard is a reflector 42.

Surrounding the body 30 and securely fixed thereto is a protectivejacket 44 of relatively light sheet metal having a frustoconical shape.At its smaller end, the jacket 44 is formed with an inturned flange 45overlying the upper end of the body and fixed thereto. as by means ofone or more screws. 46. The upper surface of the flange 45 is smoothlymachined to effect 'a tight seal with the stop shoulder 25 of thecanopy. When the fixture 22-is mounted on the latter, the sealedrelation between the flange 45 and the shoulder 25 is maintained as bymeans of one or more thumb screws 48 which lock the body 30 to thecanopy skirt 26.

Provision is made in the construction of the body 30 for readilydissipating into the surrounding atmosphere internal pressue due, forexample, to an explosion caused by a short circuit within the fixture22, while at the same time precluding the passage of flame through thewalls of the body. This is accomplished by forming at least a portion ofthe body wall structure of porous In the present instance, the body 30is fashioned with an annular window panel 49 of porous metallic materialsuch as sintered bronze particles (Figs. 1, 3, and 7). The window panel49 is interposed between and imbedded :within'ashort lip 50 at the baseof the sleeve like portion of the body and the threaded flange 32.Preferably, these members are reinforced as by means of a plurality of.circumferentially spaced ribs 51 overlying the window panel 49 (Fig.3). With the foregoing arrangement, the entire body .31) maybe fashionedas an integral piece,

.the window panel 49 being first inserted into amold so that the bodycan be cast about it. To permit venting of gases which might have passedout of the body 30 .via the'porous panel 49, narrow annular gap 52 isprovided between the protective jacket 44 and the globe ring 34.

For thepurpose of .efiecting automatic connection or disconnection of.the electrical elements of the fixture 22 and thecanopy 21 as anincident to the mechanical step of attaching the fixture .to ordetaching the same from the canopy, the unit 20 is equipped with adetachable terminal assembly of the type more fully disclosed in mycopending application Serial No. 175,419, filed July 22, 1950, nowPatent No. 2,715,214. For the present, it might be noted that suchassembly includes the terminal block 28 fixed within the canopy and aterminal block 54 mounted within the body 30 of the fixture. The block28 has associated therewith contact elements in the 'form of resilientprongs 55, 56 while the block 54 has fixed thereto contact elements inthe form of a center contact pin 58 and a surrounding contact ring 59respectively adapted to make contact with the prongs 55, 56. The pin 58and ring 59 are, in turn, connected via spring 60 and resilient plate 61to the terminals of a shock absorbing lamp receptacle 62 located withinthe chamber 39. Such receptacle conserves the longevity of the lamp 40not only when the fixture is attached to the canopy but also when thefixture 22 is detached and subjected to separate handling.

Means is provided for precluding exposed arcing as an incident toconnection or detachment of the fixture 22 from the canopy 2-1. This isaccomplished by a novel correlation of the detachable terminal assemblywith the canopy and the body 30 of the fixture. In furtherance ofsuchobjective, the terminal block 54 is nested well within the body 30 andsubstantially below the upper end thereof, being secured by the threadsof the upper body portion 31 together with transverse abutment 64 andset screw 65. By the same token, the terminal block 28 is nested withinthe skirted portion 26 of'the canopy 21. By reason of the foregoingconstruction, initial abutment between or final separation of thecontact elements 55, 56, on the one hand, and the contact elements 58,59, on'the other hand, cannot begin to occur without substantialthreaded engagement between the fixture body 30 and the canopy skirt 26(see Fig. 4). To insure complete safety, at least five full threads areengaged between'the body. 30 and the canopy skirt 26 before initial 7tact elements of the fixture and the canopy. Consequently, at theinitiation of threaded engagement between these parts, a substantial airgap exists between their mating contact elements.

Turning now to'Figs. 8 to 10, inclusive, it will be noted that there isshown a modified. explosion-proof lighting unit 20A embodying certainaspects .of the present invention and comprising a canopy 21A generallysimilar to the canopy 21, together with a fixture 22A detachably securedthereto. The unit 26A houses a modified form of detachable terminalassembly-including terminal blocks 66, 67, mounted respectively on thecanopy and the. fixture, together with a shock absorbing lamp receptacle68. The fixture 22A is organized upona sleeve-like body 69 which in thisinstanceis entirely of porous metallic constructionandpossesses flamearresting properties. Thus in the event of an arc and an explosionwithin the fixture, the body 69 is adapted to permit dissipation of theresulting internal pressure into the surrounding atmosphere whileprecluding the'passage of any flame through its walls. The upper endportion of the body 69 is threaded as at 70 for engagement with thecanopy skirt 71, such parts being lockable in threaded engagement by oneor more retaining thumb screws 72. The lower end portion of the body 69flares outwardly, being formed with peripheral threads 74 which. engageglobe ring 75. Disposed in surrounding relation with the body 69 andportion of the globe ring 75 isa protective jacket 76 having one or morevent slots 78'therein for dissipating gases which may have filteredthrough the walls of the body 69 as a result of 'an'explosion within thefixture. Clampingly secured to the flared lower end portion of the body69 by the globe ring 75 and a gasket 79 is a globe 80 similar to theglobe 38. The globe ring 75 .also carries a guard 81 and a reflector 82.

While the terminal assembly of the modified unit 20A is of the slip ringand spring loaded plunger type, the arrangement of its terminal blocks66, 67 is correlated with the dimensions of the canopy 21A and the upperportion of the body 69 so that exposed arcing incident to connection ordetachment of the fixture 22A from the canopy 21A will be precluded.This is accomplished by reason of the fact that initial abutment orfinal separation between contact elements 84, 85 of terminal block 66and elements 86, 88 of terminal block 67, cannot take place withoutsubstantial threaded engagement between the upper end of the body 69 andthe canopy skirt 71.

I claim as my invention:

1. An explosion-proof lighting unit comprising, in combination, asupporting canopy having athreaded peripheral skirt, a flame arrestingdetachablebody having a threaded metallic portion engageable withsaid-skirt, said body also having anotherthreaded portion engageablewith globe clamping means, means defining a closed explosion-proof lampchamber within said detachable body, a first terminal block fixed tosaid canopy, a second terminal block fixed to said body, relativelymovable contact members carried by said terminal blocks and adapted toabuttingly engage each other, the relative dimensions of said body andthe location of said terminal blocks being such that an abuttingrelationship between said contact members can be neither established norbroken without substantial threaded engagement between said threadedmetallic portion of said body and said canopy skirt.

2. An explosion-proof lighting unit comprising, in combination, asupporting canopy having a depending threaded skirt, a flame arrestingdetachable metallic body having a threaded portion engageable with saidskirt, a globe attachable to said detachable body and defining therewitha closed explosion-proof lamp chamber, electrical contact elements fixedto said canopy, mating electrical contact elements fixed to said bodyoutside said closed explosion-proof lamp chamber, the relativedimensions of said body together with said canopy and said contactelements being such that an abutting relationship between said matingcontact elements can be neither established nor broken withoutengagement of at least five full threads between said threaded portionof said body and said canopy skirt.

3. .In an explosion-proof lighting unit, the combination comprising asupporting canopy having a threaded portion, a flame arrestingdetachable body including at least a portion of porous metallicmaterial-and having means susceptible of threaded engagement with saidcanopy, means defining. a closed explosion-proof lamp chamber withinsaid detachable body, a .first terminal block fixed to said canopy, asecond terminal block fixed to. said body, contact elements mounted onone of said terminal blocks, coacting contact elements mounted ontheother of said terminal blocks, said contact" elements beingsusceptible of entering into abutting engagement with each other as anincident to attachment of said body to said canopy, said terminal blocksbeing located on said canopy and said body in posf ions wherein asubstantial air gap exists between respective ones of said coactingcontact elements at the initiation of threaded engagement between saidbody and said canopy.

4. An explosion-proof lighting unit comprising, in combination, asupporting canopy having a depending threaded skirt, a hub-like bodyhaving a threaded portion engageable with said skirt, said body alsohaving a flame arresting rigid window panel of porous metallic materialintegral therewith, a globe fixed to said body and defining a sealedlamp chamber therewith, electrical contact elements carried by saidcanopy, mating electrical contact elements fixed to said hub-like body,the relative dimensions of said body as well as said canopy and saidcontact elements being such that an abutting relationship between saidmating contact elements can be neither established nor broken Withoutsubstantial threaded engagement between said body and said canopy skirt.

5. In an explosion-proof lighting unit, the combination comprising asupporting canopy having a depending threaded skirt, a metallic hub-likebody having a flame arresting rigid window panel of porous metallicmaterial integral therewith and having means susceptible of threadedengagement with said canopy, contact elements carried by said canopy,coacting contact elements carried by said body, said contact elementsbeing susceptible of entering into abutting engagement with each otheras an incident to attachment of said body to said canopy, said body andsaid canopy being so correlated with said contact elements that asubstantial air gap exists between respective ones of said coactingcontact elements at the initiation of threaded engagement between saidbody and said canopy.

6. An explosion-proof lighting unit comprising, in combination, asupporting canopy having a threaded skirt, a sleeve-like body of flamearresting porous metallic material having a threaded portion engageablewith said skirt, a globe attachable to said body, electrical contactelements fixed to said canopy, mating electrical contact elements fixedto said sleeve-like body, the relative dimensions of said body as wellas said canopy and said contact elements being such that an abuttingrelationship between said mating contact elements can be neitherestablished nor broken without substantial threaded engagement betweensaid body and said canopy skirt.

7. In an explosion-proof lighting unit, the combination comprising asupporting canopy having a threaded portion, a sleeve-like body of flamearresting porous metallic material and having means wsceptible ofthreaded engagement with said canopy, first terminal block fixed to saidcanopy, a second terminal block fixed to said body, contact elementsmounted on one of said terminal blocks, mating contact elements mountedon the other of said terminalblocks, said contact elements beingsusceptible of entering into abutting engagement with each other as anincident to attachment of said body to said canopy, said terminal blocksbeing located on said canopy and said body in positions wherein asubstantial air gap exists between respective ones of said matingcontact elements at the initiation of threaded engagement between saidbody and said canopy.

8. For use in an explosion-proof lighting unit, a body comprising, incombination, a sleeve-like portion terminating in a narrow lip, asurrouding flange, an annular Window of porous metallic materialinterposed between and imbedded within said lip and said flange, and aplurality of circumferentially spaced ribs connecting said flange andsaid sleeve-like portion, said ribs being integral with said flange andsaid sleeve-like portion.

9. An explosion-proof lighting unit comprising, in combination, asupporting canopy, a hollow body attachable to and detachable from saidcanopy, means adjacent the upper end of said hollow body and extendingtransversely thereof for preventing the passage of gas through saidhollow body, a globe attached to the lower end of said hollow body ingas tight relation thereto and defining therewith and with said means aclosed lamp chamber Within said hollow body, and a porous metallicwindow integral with said hollow body and constituting a flame arrestingportion therein, said hollow body, said means, and said globe beingattachable to and detachable from said canopy as a unit withoutviolating the closed condition of said lamp chamber.

References Cited in the tile of this patent UNITED STATES PATENTS489,150 Keil Jan. 3, 1893 1,787,032 Benjamin Dec. 30, 1930 2,304,085Griflin Dec. 8, 1942 2,530,135 Thornblom Nov. 14, 1950 FOREIGN PATENTS640,250 France Mar. 24, 1928 444,877 Great Britain Mar. 31, 1936

